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Various plates of the Earth's crust shift, due to the molten rock lying beneath them, this causes them to collide and spread out. This movement forces the molten rock to move upwards and come out on the surface thus forming volcanoes. It is because of this that most volcanoes are located on the edges of the Earth's crustal plates. The name Volcano is derived from the name of an island called 'Volcano' in the Mediterranean sea, which was formed due to a Volcanic eruption.

More than 800 active volcanoes exist all over the Earth, mostly located in the Pacific ocean region. The molten rock which erupts from volcanoes is called 'Magma'. Gases including sulphur, carbon dioxide and water vapour below the crust expand and force the magma upwards and it erupts fromm the gasps in the Earth's crust. The escaping molten rock is called 'Lava', it has a temperatur of about 1,000 degree centigrade, and is capable of melting steel.

Igneous rocks are produced as a result of the cooling of volcanic lava. The shape of a volcano depends upon the type of magma it produces i.e. magma of a thinner consistency produces a relatively flatter volcano whereas thick magma produces a volcano which has a steep, inverted, cone. There are some volcanoes which throw up large quantities of ash, as result of which they have cones largely made up of ash. Volcanoes are either 'Active' or 'Extinct'. Active colcanoes erupt in spurts on various volcanoes and between eruptions they are called as Dormant volcanoes on the other hand had erupted thousands of years ago and have stopped erupting since then. The Mt. Vesuvius erupted in the 79 A.D. when it buried the city of Pompeii and then it erupted in the year 1944. One of the greates volcanic eruptions occured on the island of Krakatoa in Indonesia in the year 1883. One of the other volcanic wonders is the formation of the island of Surtsey, near Iceland, in 1963.